I've used Krita for around 3 years. In my opinion, it's a great stepping stone for intermediate artists to Photoshop- the industry standard for digital art. This is not a program for beginning digital artists. (I suggest roughly going from MSPaint → FireAlpaca → PaintToolSAI/Gimp/whatever → Krita → Photoshop)

CONS
Just putting this out here front and center so if any of these are a deal breaker, you don't have to waste time reading the rest.
• Does not handle big files well
• Adjustments does not have sliding scales, they have this thing that I honestly don't even know what is going on
• Reference section is god AWFUL. Do yourself a favor and get PureRef instead.

PROS
• IT'S 100% FREE compared to Photoshop's $10/month. If you're under 15 and can't get a job/ don't want to pay every month, get Krita!
• Supports many files, including gif, png, jpeg, pdf, etc.
• Has different interfaces for your needs, including vector, paint, animation
• Wide range of decent brushes, wide range of layer types
• Documents customization
• Best feature is the HOTKEY SHORTCUTS. Krita is made for painting FAST. If you aren't using the hotkeys, what are you even downloading Krita for??? Make your non-dominate hand useful for once!

So if you're a broke bitch and want to have a similar experience to Photoshop and paint real fast, get Krita.